New Methods Realized For Imaging The Center Of The Milky Way

Astronomers may now have a way to image the center of the Milky Way galaxy, which has posed problems to scientists trying to image all of its exotic features. Soon they may be able to learn more about the features of the center of the Milky Way and learn more about where they are located in the galaxy by use of radio waves.

Prior to the discovery of radio waves, astronomers primarily used optical waves like the X-ray and infrared wavelengths. This was done because it is unusual to see any dark feature with radio waves. However, Farhad Zadeh, Northwestern University professor of physics and astronomy and member of Northwestern´s Center for Interdisciplinary Exploration and Research in Astrophysics, discovered that radio images can detect dusty clouds and stars by simply taking a picture using radio waves.

Because the radio is a long wavelength, it does not get as easily absorbed thus it passes through whatever is in its way. For this reason, Zadeh initially assumed that the dark features in the radio pictures he was studying were nothing. With some attention to detail, however, the professor found that the features must have been those belonging to five previously known dense molecular and dusty clouds located in the center of our galaxy, even some near Sagittarius A*, our galaxy´s black hole.

Through his discovery, Zadeh is the first to identify what he is calling radio dark clouds and stars–those that radio wavelengths were able to image but were not imaged prior to this. This allows astronomers to better understand the galaxy and what is in it. “When you see these dark stars or clouds in radio wavelength images, it tells you something very interesting,” Zadeh said in a statement. “We immediately know there is a cold gas cloud or dusty star mixing with a hot radiative medium and that an interaction is taking place. Knowing details of these clouds is important because the clouds can produce stars and also provide material for the growth of black holes.”

The interaction between a cold dust cloud and a hot radiation field results in a loss in the continuum emission. Because of that result, these appear as a dark feature in the radio wavelength, which provide astronomers with the size of the cloud in three dimensions.

Because the technique provides very good sensitivity of faint dusty features, it produces images that have even higher resolution than many other optical telescopes. The radio wave pictures work as an initial observation telling astronomers what needs to be studied more closely. Plus, astronomers can measure the size of dusty stars using this technique.

According to Zadeh, a good example of a dusty cloud that could be imaged using his technique of radio waves is G2, a tiny cloud fast approaching Sagittarius A*. Even though the dusty cloud is now too close to the black hole for a radio wavelength picture, Zadeh is looking at earlier data to try and locate G2 as a radio dark cloud.

Professor Farhad Zadeh will present the results from his study on radio wave imaging at the 221st meeting of the American Astronomical Society today, January 8. He will also participate in a press conference on the galactic center following his presentation at 12:45pm PST (3:45pm EST).